Stitch interrupting device for sewing machines

Abstract

A device for interrupting the formation of stitches in a sewing machine having at least two needles and a looper for each needle which are arranged to be actuated in tandem. The needles are phased to perform their functions simultaneously with a first having an elongated thread opening, and the second a conventional opening. The first needles' looper is slightly elevated and if no lack of phasing exists between the needles and their loopers, the elevated looper will cooperate with its needle adjacent the upper end of the thread hole and the other looper cooperates with its needle in a conventional manner. Should there be a lack of phasing, the elevated looper cooperates with its needle midway between the length of the thread hole which causes the other looper to pass beneath the hole of its needle thus interrupting the formation of stitches by the latter needle.

We claim: 
     
       1. A device for interrupting the formation of at least one line of stitching in a sewing machine of the type having a support structure for pivotably supporting at least two looper holders in tandem with individual loopers mounted on each holder and at least one needle in operative association with each looper for forming spaced and parallel lines of stitching, said device comprising: a. means defining an elongated thread hole in one of the needles;   b. means for elevating that looper associated with the needle having the elongated thread hole on its looper holder to an operating level above the looper with which it pivots in tandem; and   c. means for displacing the points of pivot of said looper holders for effecting continued formation of stitches by the combination of the needle with said elongated thread hole and said elevated looper, and a cessation of stitches by the other needle and its looper.   
     
     
       2. The structure according to claim 1 wherein said elevating means defines a spacer assembled intermediate the looper holder and the looper operatively associated with the needle having said elongated thread hole. 
     
     
       3. The structure according to claim 1 wherein said displacing means defines a pneumatic cylinder having a piston operatively connected to both said looper holders for effecting simultaneous displacement of both the loopers. 
     
     
       4. The structure according to claim 3 wherein said device includes a coil spring for returning the looper holders and loopers to their initial positions upon a cessation of air into said pneumatic cylinder.